Many compositions and methods for chemical-mechanical polishing (CMP) the surface of a substrate are known in the art. Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) for polishing metal-containing surfaces of semiconductor substrates (e.g., integrated circuits) typically contain abrasives, various additive compounds, and the like, and frequently are used in combination with an oxidizing agent. Such CMP compositions are often designed for removal of specific substrate materials such as metals (e.g., tungsten or copper), insulators (e.g., silicon dioxide, such as plasma-enhanced tertraethylorthosilicate (PETEOS)-derived silica), and semiconductive materials (e.g., silicon or gallium arsenide).
In conventional CMP techniques, a substrate carrier (polishing head) is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure (down force) to urge the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typical abrasive materials include, for example, silicon dioxide (silica), cerium oxide (ceria), aluminium oxide (alumina), zirconium oxide (zirconia), titanium dioxide (titania), and tin oxide.
The abrasive desirably is suspended in the CMP composition as a colloidal dispersion, which preferably is colloidally stable. The term “colloid” refers to the suspension of abrasive particles in the liquid carrier. “Colloidal stability” refers to the maintenance of that suspension during a selected period of time with minimal settling. In the context of this invention, an abrasive suspension is considered colloidally stable if when the suspension is placed into a 100 mL graduated cylinder and allowed to stand without agitation for a period of time of about 2 hours, the difference between the concentration of particles in the bottom 50 mL of the graduated cylinder ([B] in terms of g/mL) and the concentration of particles suspended in the top 50 mL of the graduated cylinder ([T] in terms of g/mL) divided by the initial concentration of particles suspended in the abrasive composition ([C] in terms of g/mL) is less than or equal to about 0.5 (i.e., ([B]−[T])/[C]≦0.5. The value of ([8]−[T])/[C] desirably is less than or equal to about 0.3, and preferably is less than or equal to about 0.1.
U.S. Pat. No. 5,527,423 to Neville et al., for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface of the metal layer with a polishing slurry comprising high purity fine metal oxide particles suspended in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 to Cook et al. discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 to Bruxvoort et al. discloses a fixed abrasive polishing pad.
For copper CMP applications it often is desirable to use a relatively low-solids dispersion (i.e., having an abrasive concentration at a total suspended solids (TSS) level of about 1 percent by weight or less), which is chemically reactive toward copper. Chemical reactivity can be modulated through the use of oxidizing agents, chelating agents, corrosion inhibitors, pH, ionic strength, and the like. Balancing the chemical reactivity and mechanical abrasive properties of the CMP slurry can be complicated. Many commercial copper CMP slurries are highly chemically reactive, and exhibit high a copper static etch rates (SER) of well over 100 Angstroms-per-minute (Å/min), which can be controlled, at least in part, by organic corrosion inhibitors, such as benzotriazole (BTA), triazoles, and imidazoles. Such compositions often do not have good corrosion control after polishing, however. Common commercial copper CMP slurries also frequently suffer from dishing-erosion, defectivity, and surface topography problems.
Another metal of interest in semiconductor applications is silver, which shares many properties and characteristics in common with copper vis-à-vis CMP, such as corrosion properties and passivating properties. For example, both silver and copper effectively form films with and are passivated by benzotriazole. In addition, Cu and Ag both readily dissolve in acidic pH with a formation of metal ions (for Cu, Cu+1 and Cu+2 and for silver Ag+1) and passivate at higher pHs with a formation of oxides.
There is an ongoing need to develop new CMP compositions and methods utilizing relatively low-solids CMP slurries with a reduced level of dishing-erosion and defectivity, relatively high copper and/or silver removal rates, as well as superior corrosion protection and surface inhibition compared to conventional CMP slurries. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.